Temperature resistant body



July 17, 1962 M. G. WHITFIELD ETAL 3,044,156

TEMPERATURE RESISTANT BODY Filed June 25, 1954 EGJ.

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United States Patent O 3,4i,156 TEMPEEEATURE RESSTANT BDY lvlarshall G.Whiteld, 2 Harvard St., Garden City, NX., and Victor Sheshnnoii, P). Box'702, lviagnelia, Ark. Fiied .inne 23, 1954i, Ser. No. 438,652 7Ciaiins. ttll. 29-194) The present invention relates to improved metalbodies constituted of tungsten or molybdenum and ferrous alloys thereof,and more particularly to metal bodies containing substantial percentagesof tungsten and molybdenum protected against deterioration inV oxidizingatmospheres at high operating temperatures.

This is a continuation-in-part of our copending application, Serial No.673,880, filed lune l, 1946, and entilted Oxidation Protected Tungstenand Molybdenum Bodies and Method of Producing Same, which has nowmatured into Patent 2,682,101, dated lune 29, 1954.

At the present time there are various industrial. developments wherealloys of special character are necessary, capable of retaining theirhigh mechanical strength at high operating temperatures. Examples ofsuch applications are particularly parts for jet engines and gasturbines in which the demands made on the structural parts with respectto their strength at elevated operating temperatures are extremelyexacting.

Materials now employed for these purposes generally comprise alloys ofiron and of nickel, in many cases with additions of cobalt, chromium,tungsten and molybdenum. Even the alloys of tungsten and molybdenum,while theoretically promising, proved very disappointing in actualpractice. ln general, few, if any, of these alloys had a useful lifeover 300 hours, necessitating frequent replacement of criticallyimportant structural elements at great trouble and expense.

As is known, tungsten and molybdenum are unstable when heated in air orin any other oxidizing atmosphere at temperatures in the range of 800C., or above. The oxides formed on the surface of the tungsten andmolybdenum bodies under such conditions sublime or boil awaycontinuously V't0 such a pronounced degree that these metals can only beused in a pure reducing atmosphere of hydrogen, or of an inert lgas,such as argon, or in vacuum. The same difficulty is present with respectto alloys containing more than of tungsten and molybdenum. Of course,this circumstance greatly restricted or even negatived the usefulness orsuch metal bodies and, as a matter of fact, those skilled in the artstrongly advised against the use of alloys containing tungsten andmolybdenum in excess of 15% for high temperature applications. Althoughthe outstanding problem was well known in the art and from time to timevarious suggestions and proposals were made to provide a solutiontherefor, none, as far as we are aware, of these suggestions andproposals was completely satisfactory and successful on a practical andindustrial scale.

We have found that the problem may be solved in a remarkably simple andunique manner.

It is another object of the inventionV to provide a novel and improvedmethod of preventing the surface sublimation and resulting deteriorationof metal bodies constituted of tungsten, molybdenum, and alloys thereofwhen exposed Yto oxidizing atmospheres at elevated temperatures in therange of 800 C. and thereover.

It is a further object of the invention to provide a protective layer onthe surface of tungsten and molybdenum bodies, said protective layerbeing essentially composed of an aluminum containing material.

It is also within the contemplation of the invention `to provide a novelmethod of protecting tungsten and molybdenum bodies against surfacesublimation at high operating temperatures while exposed to oxidizingdlh Patented July l?, 1962 r ice j vmeans for avoiding the deteriorationof protected bodies made `of or containing molybdenum or tungster orboth due to excessive differences in coeicients of expansion as betweenthe body and the coating.

Another object of the invention is the provision o coated bodies of thegeneral class herein referred to in which beryllium is a constituent ofthe body or the coating or both.

Other and further objects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawing, in which:

FIG. l is a fragmentary sectional vview of a metal body embodying theprinciples of the invention during the process of its manufacture.

FIG. 2 is a similar View of an oxidation protected tungsten ormolybdenum body having a bonding layer of nickel and a protective layerapplied thereto, and

FIG. 3 is a longitudinal sectional view of a refractory metal bodycomprising a core of tungsten or molybdenum and having a partially`diffused protective layer thereon constituted of an alloy of protectiveelements and molybdenum or tungsten..

Y Broadly stated, according to the principles of the inf vention,thetungsten or molybdenum bodies to be protected are .coated preferablywith a aluminum base-Inaterial which maybe pure aluminum or alloys richin aluminum. This coating may be carried out by various procedures butbest results are obtainedby a hot dip method in which the metal bodiesto `be protected are immersed in a bath of molten metal for apredetermined length of time sufficient to provide a coating of themetal thereon. We have found that by this method there is formed a thinprotective layer on the surface of the tungsten or molybdenum body whichlayer is essentially constituted of an alloy of coating metal with thebase metal. Experimental work with tungsten and molybdenum bodiestreated in accordance with the invention has indicated that thesematerials do not exhibit their normal oxide forming characteristics evenat temperatures approximating the boiling point of aluminum and in manycases even at vtemperatures as high as 2000 C.

The bath of molten aluminum base material may be composed of high purityaluminum, commercially pure aluminum and of aluminum alloys having arelatively high aluminum content. Examples of such aluminum alloys arealloys containing 5% to 15% by weight of at least one of the elementsselected from the group consisting ofiron, nickel, chromium, cobalt andberyllium, the balance being substantially all aluminum. In addition,various other aluminum base materials containing other and furtherconstituents may be used..

'If desired, the bodies to be treated' with the bath of molten aluminumbase material may be subjected to a preliminary cleaning bySandblasting, burnishing and similar mechanical procedures. In mostcases, however, such preliminary cleaning is not necessary. For example,rolled molybdenum sheet may be subjected to treatment by the bath ofaluminium base material without any preliminary cleaning.

.The temperature of the bath of molten aluminum base material may besubject to considerable variations in Vinitial temperature of the bodiesto be treated, on their thickness or mass and to some extent also on theoperating temperature of the bath. The thickness of the coating ofaluminum basematerial is not critical but may be in the order of 0.002."to 0.00.4".

ExaminationV of wire and sheet samples of .tungsten p and molybdenum,which have been treated with aluminum and exposed tohigh temperatures inoxidizing atmos-v -pheres, indcatestha't a high melting compound ofaluminum .with the tungsten or molybdenumcorehas been` formed and thatthis alloy is free from the weness of either thev tungsten or molybdenumwith regard to oxidizing tov form .a compound of low boiling orsublimation point on the surface. .For example, samples treated'iby themethod of the invention have been heated Vto tempera- Atures a hundreddegrees C. above the normal .boiling point Yof'aluminum before thealuminum boiled away, indicating that the alloysof aluminum withtungsten or molybdenum'have extremely high Vboiling orsublimationpoints. Likewise, it has been found'that the presence Vofaluminum on thesurfaceofthesemetals, will permit their use for.applications requiring substantial strength at `elevated temperatures.The method of the invention is applicable with equal or similar resultsalso to alloys of at least one of the metals iron, nickel, cobalt withtungsten or molybdenum, or'both, containing substantial quantities oftungsten ormolybdenum, such as at leastl 15% by weight, Vand Valso toalloys of tungsten and molybdenum.

v Preferably, the aluminum coated tungsten and molybdenum containingbodies are ,heat treated'to assureV the formation lofa high meltingcompound of aluminum with the tungsten or molybdenum core and thereby.to obtain a completely stable product. Itis also possible, however, toomit-such' heat treatment andto rely on the diffusion of the aluminumcoating into the refractory core during.V

'the actual operation at elevated temperatures. .If 'heat treatment isresorted to, the heat treating temperature may Abe in the order of 1300"C., although it is not restricted to 'such temperature.

in many cases copper and silver plates may provide equal 1 or similarresults.

While theexact reason for the beneficial effect `of the v preliminarydeposit of nickel or other iron group metal is not fully understood, itis believed that these metals form alloys with aluminum more quicklythan do tungsten and molybdenum and that these electrodeposited filmsact as temporary protectors until the aluminum can form its alloy withthe tungsten or molybdenum which have a tendency to oxidize even atrelatively low temperatures, such as red heat."

Referring now to the drawing, in FIG. l there is shown a metal bodyembodying the principles of the invention which comprises a base or core10 of tungsten or molyb denum. Upon both faces .of the core there isprovided a thin coating 11 of aluminum or aluminum base materialconstituting a protective layer for the core. Of course, in actualmanufacture, layer 11 is initially a coating of aluminum containingsometungsten or molybdenum and is bonded to the core by an aluminum richalloy of these refractory metals caused by partial diffusion of thealuminum into the core. In service, or in the final stage ofmanufacture, the excess `aluminum is partly oxidized and partly diffusedto produce the alloy surface layer which is referred to in theforegoing. K

FIG. 2 illustrates an example of the modification of the 'invention inwhich the tungsten or molybdenum core 20 is first coated with a thiniilm of nickel or other iron base metal 2l and thereafter is exposed tothe eect of a molten bath of aluminum base material, such as, forexample, commercially pure aluminum, thereby forming a protectivelayerZZ onV the exterior Aof the core. As arresult of the interaction ofthe core material With that of the layers `21 and 22 during the heatingand coating'treatments and .'"While the methodoffthe invention providesVexcellent v. results in protecting and stabilizing tungsten and molyb-`denum bodies, when .treating these metals with `aluminum or its alloys,occasionally small spots or areas are found which are ralloyed only withextreme ditiiculty. VWe .have found that 4this diiculty may becompletely avoided by electrodepositing a thin film Vorrlayer ofnickelron the V,surface of ther tungsten or molybdenum and diffusing orY at leastheating the nickel plated sections in a non-oxidizing orreducing atmosphere at approximately .l000 C.y

with aluminum. This modification of the methodl of the 'before treatingthe sections of tungsten or molybdenum Y The thickness of theelectrodeposited nickel layer is v not criticaland maybeasubjected toconsiderable Vvariations. In this connection, it may be observed thatdijlul sion of the nickel layer maybe accomplished not only by layer isaccomplished by the heating eiect of the bath of aluminum base material,and the bath at the same time provides the non-oxidizing or protectiveenvironment.

It has been found that nickel is not the only metal which subsequentservice operation, the metal body is converted into the one shown inFIG; 3 wherein the individual existence` of layers Zyl and 22-haspractically disappeared, such layers being combined intoa layer 23`which is composed of an alloy rich in aluminum and-containingappreciableamounts of nickel and tungsten or molybdenum.

While in the drawing fragmentary sectional views of 1 refractory metalstrips are shown which are coated with a layer of aluminum base materialon both facesthereof, in actual practice, the refractory metal bodiesare provvidedwith a protective layer of the described characterthroughout their entire surface, including their ends and edges. In thismanner, the said metal bodies are fully protected from Ydeterioration atelevated operating tem- '.peratures.

In order to facilitate understanding of the invention by those skilledin Athe art, the following illustrative examples may be given:

' having a temperature of 720 C., for 6 minutes. After removal from thebath and cooling, the materialwas tested by heating it to 1400-1500 C.in an oxidizing atmosphere for 4 hours, without noting `any appreciabledeterioration.

' Example II A. molybdenum sheet about 0.020" thick was cleaned and alight coating of nickel was electrodeposited thereon. The plated sheetwas heated for a few minutes in a reducing atmosphere at approximately1000" C. The sheet was .cooled and then treated by immersing in a bathof molten commercially pure aluminum, having a temperature of 740 C.,for 3 minutes.

Although the present invention has been described in with each other orwith other metals. The advantages of the invention in the case oftungsten and molybdenum alloys are particularly accentuated when suchalloys contain at least by weight of tungsten or molybdenum, or tungstenand molybdenum combined.

The teachings hereinabove made and the `examples hereinabove given,applying to the coating of tungsten or molybdenum bodies (as defined)with aluminum or aluminum alloys (as dened), apply as well to the use ofthe metals silicon and beryllium as constituents of the initial coating.One of the purposes of the present invention is to avoid extraordinarydiscrepancies between the coefficients of expansion of the base metaland the coating material. As compared with aluminum which has a highcoefficient of expansion, tungsten and molybdenum bodies have relativelylow coeihcients of expansion.

it has hitherto been known that the alloying of relatively largequantities of silicon with aluminum will provide a metal compositehaving a relatively lower coeicient of expansion, and in particular acoefficient of expansion substantially closer to that of ferrous bodies.For such purposes, as much as from 25% to 30% or more of silicon hasbeenalloyed with aluminum.

It has been found, however, that such very large quantities of silicongive an aluminum alloy material which is more difficult to use in molten`form as a hot dipping medium, and also that the formation of anadequate bond between the alloy layer and ferrous base metals isrendered more dicult.

Beryllium is a metal which has a coetiicient of expansion substantiallyless than half that of aluminum. We have found that beryllium may bealloyed withaluminum to provide alloys having coetlcients of expansionmuch closer to that of ferrous bodies and tungsten and molyb\ denumbodies as herein dened. When beryllium is added to aluminum, it isreadily possible to secure coating alloys having coeiiicients ofexpansion very much lower than that of aluminum alone, and in particularcoefficients of expansion substantially corresponding with those ofconventional ferrous bodies, with the beryllium within the ranges setforth above, namely from about 5% to about 15%, and up to about 50% ofthe alloy.

It is readily possible to employ beryllium along with silicon., Forexample, an alloy can be formed of aluminum containing about 5% to 15%of beryllium and 5% to 50% silicon, balance being aluminum.

Beryllium in substantial quantities thus is seen to be a valuablecomponent of aluminum or aluminum alloys used for coating where theobject is to attain in the coating a coeicient of expansion much morenearly corresponding to that of the base metal, whether the base metalis to be coated by hot dipping or by the casting of the alumi-` numalloy against it. Moreover, beryllium has a substantially lessenedtendency to interfere with the formation of a strong bond between thealuminum alloy and the base metal upon which it is coated.

In the formation of tungsten or molybdenum bodies which are to withstandoxidative deterioration at the high temperatures mentioned herein, theberyllium does not interfere with the action hereinabove described. Infact, tungsten and molybdenum bodies, resistant to oxidativedeterioration at high temperatures, can be produced by coating tungstenor molybdenum bodies (as deiined) with beryllium alone, in spite of thehigh avidity of the last named metal for oxygen. The use of interface Ametal coatings as hereinabove disclosed between the aluminum alloy' andthe base 'metal is equally veffective with beryllium alone or withvaluminum alloys containing beryllium or beryllium and silicon.

In the production of coated bodies having a minimum difference betweenthe coefficients of expansion of the bodies `and the coatings thereon,it is possible not only to diminish the coeicient of expansion of thecoatings, but also to raise the coetiicient of expansion of the bodies.Where tungsten and molybdenum bodies are spoken of above, not only arebodies of pure molybdenum or tungsten or mixtures of the twocontemplated, but also ternary or complex alloys containing at leastsubstantially 15% of tungsten or molybdenum or a mixture of the two. Thecoefficient of expansion of such ternary or complex alloys is higherthan that of molybdenum or tungsten alone. But it is possible to raisethe coetlcient of expansion of such bodies by alloying the molybdenum ortungsten or ternary alloys containing them with such elements aschromium. This may ordinarily be done without sacrice of desirablephysical properties.

When coating tungsten or molybdenum or ferrous bodies with beryllium oraluminum alloys containing beryllium, a protective `atmosphere willnormally be maintained over the bath'since beryllium is more subject tooxidation than aluminum.

Modications may be made in the invention without departing from thespirit of it. The invention having been described in certain exemplaryembodiments, what is claimed as new and desired to be protected byLetters Patent is:

l. A body formed from metal chosen from a class consisting of tungsten,molybdenum, mixtures of the two, Kand ferrous alloys containing at least15 of any of the foregoing, bot coated with a bonded layer of aluminumcontaining substantially 5% to 50% beryllium.

2. A body formed from metal chosen from a class consisting of tungsten,molybdenum, mixtures of the two,

'an-d ferrous alloys containing at least 15% of anyy of the foregoing,hot coated with a bonded layer of'aluminum containing substantially 5%lto 15% beryllium, and substantially 5% to 15% silicon.

3. As a new article of manufacture, a refractory metal tbody protectedfrom surface deterioration Iat lelevated operating temperaturescomprising la core constituted of a refractory metal selected from thegroup consisting of tungsten, molybdenum, alloys of tungsten andmolybdenum, and alloys containing at least 15% of any of the foregoingwith at least yone of the metals iron, nickel, cobalt and chromium, and`a protective layer on said core of aluminum containing substantially 5%to 15% beryllium.

4. As a new `article of manufacture, a refractory metal body protectedfrom surface deterioration at elevated operating temperatures comprising-a core constituted of a refractory metal selected from the groupconsisting of tungsten, molybdenum, alloys of tungsten and molybdenum,and `alloys containing at least 15% of any of the foregoing with atleast one of the metals iron, nickel, cobalt and chromium, Iand `aprotective layer on said core of aluminum containing substantially 5% to15 beryllium, and substantially 5% to 50% silicon.

5. The structure claimed in claim 3, with a thin inter- (References onfollowing page) 'Y ff Referenes' cited in the fue df this patent YVUNITEDswmgs VPATENTS,

`Mml: Sept. n 28, 1915 Archer ..l June 11, 1929- Weiger May 31,1932VHorselcl Sept. 27, 1932 Nook Dec. 1, 1936 Schwarzkopf Oct. 26,l 1937Kruh June 21, 1938V S Y Whie1d' Nov. 8, 1938 Sittings Aug. 28, 1951 vShepard ,Mar. 11, 1952 Campbell Ian. 12, 1954 Whiteld June 29, 1954FOREIGN PATENTS Great Britain July 8, 1926 Frame Apr. 8, 1932

1. A BODY FORMED FROM METAL CHOSEN FROM A CLASS CONSISTING OF TUNGSTEN,MOLYBEDEUM, MIXTURE OF THE TWO AND FERROUS ALLOYS CONTAINING A LEAST 15%OF ANY OF THE FOREGOING, HOT COATED WITH A BONDED LAYER OF ALUMINUMCONTAINING SUBSTANTIALLY 5% TO 50% BERYLIUM.